About 2,000 light-years away, near the constellation Cygnus, lies a fairly unremarkable star much like our own sun. Unremarkable, that is, save for the dense planetary cornucopia orbiting it. Last year astronomers using NASA’s Kepler spacecraft discovered six planets swarming the star, now called Kepler 11, of which five reside closer to their star than any planet orbits our sun.
The Kepler 11 system is fascinating—it offers a glimpse of a planet-formation process that churned out a product very different from our own solar system. It also inspired one astronomer to compose a music video.
Alex Parker, a postdoctoral researcher at the Harvard–Smithsonian Center for Astrophysics, assigned a different note to each of six planets in the Kepler 11 system. The Kepler spacecraft discovers planets by identifying transits—brief, shallow eclipses in which a planet passes in front of its star and blocks a small fraction of starlight. In the video, as the planets proceed through a sped-up animation of their orbits, each of those events produces the transiting planet’s signature note. (In other words, the planet’s note plays each time it passes through the Kepler spacecraft’s field of view.) Parker explains the methodology behind his “Six-Planet Sonata” on his Vimeo page:
Here, I've taken each transit seen by the observatory and assigned a pitch and volume to it. The pitch (note) is determined by the planet's distance from its star (closer = higher), and they are drawn from a minor 11 chord. The volume is determined by the size of the planet (larger = louder).
The minute-long piece of music draws on two years of data. During that time the outermost planet in the Kepler 11 system transited its star about half a dozen times, its note ringing out in Parker's piece each time; the closer-in planets passed through the spacecraft’s field of view more frequently and so sound their notes more often. But because the planets have different orbital periods, it would take 55 years of data for the music to repeat—when the planets return (almost exactly) to their starting positions. “In principle, it may never repeat perfectly,” Parker adds, “since the orbits change with time while the planets interact gravitationally with each other.”
This is not Parker’s first sonification of astronomical data. Last year he and a colleague turned a three-year supernova search into a “Supernova Sonata.” In that piece they assigned each of the 241 supernovae detected by the Canada-France-Hawaii Telescope a note based on the properties of the supernova and its host galaxy.